At present, as fossil fuel such as coal, petroleum, and natural gas which are being used as important energy sources is depleted, various research and developments for increasing use efficiency of energy, in particular, efficiently converting medium-low temperature heat energy (in particular, waste heat) into electric energy have been conducted.
As illustrated in FIG. 1, a thermodynamics Rankine cycle which is used to convert heat energy into electric energy has a structure in which a working fluid circulated by a pump 10 is converted into high pressure steam by passing through a boiler 20 to rotate a turbine 30 and shaft power generated by the rotation of the turbine 30 rotates a generator 40 connected to the turbine to generate electricity.
As such, in the case of using the high temperature heat source, as the working fluid, water has been mainly used and in the case of using the medium-low temperature heat source, as the working fluid which is configured of an organic Rankine cycle and thus has a low boiling point and a high vapor pressure, a Freon-based refrigerant and a hydrocarbon-based organic mixture such as propane have been used.
However, in the case of the existing thermoelectric conversion cycle, the turbine and the generator in addition to a heat exchanger are additionally mounted, and thus thermoelectric conversion efficiency is low and a size of a system is large, such that it is difficult to recover heat from various kinds of devices generating waste heat, and in particular, in the case of the medium-low temperature waste heat, it is difficult to recover heat and perform conversion into electricity.
As a method for solving the above problem, U.S. Pat. No. 7,445,101 discloses a system for circulating a magnetic fluid having magnetic particles instead of the existing working fluid (refrigerant) in a closed loop and directly performing conversion into electricity using an induction coil, in which the system is a device for spinning (rotating) magnetic particles inside a circulator which circulates the cycle by a permanent magnet to generate a current induced into an induction coil and has a difficulty in efficiently generating a flux required to draw an induction current due to a disorder occurring at the time of circulating the magnetic particles and an offset of the flux occurring by the spinning.
As illustrated in FIGS. 2 and 3, a device for generating electricity using magnetic particles according to an embodiment disclosed in U.S. Pat. No. 4,064,409 is configured to include a magnetic fluid 100 having magnetism in a nano size unit, a tube 110 which is a passage through which the magnetic fluid flows, a pump 130 which circulates the magnetic fluid 100 through the tube 110, and an induction power generation unit 200 which obtains electricity by a flow of the magnetic fluid 100.
In this case, in particular, as illustrated in FIG. 3, the induction power generation unit 200 is configured to include a silicone tube 220 through which the magnetic fluid 100 passes by the pump 130 and a solenoid coil 230 spirally wound around a predetermined section outside the silicone tube 200 to enclose the silicone tube 220 to obtain an electromotive force from induction power generated based on a Fleming's right hand rule due to the flow of the magnetic fluid 100.
The magnetic fluid 100 is a fluid in which magnetic powders having nanoparticles are stably dispersed in a liquid in a colloidal shape and a surfactant to prevent precipitation or aggregation from occurring is added. Generally, when lines of magnetic force pass through a plane which is vertical to a magnetic field and has an area A, the number of lines of magnetic force passing through a unit area is proportional to a size B of the magnetic field. Therefore, the number of lines of magnetic force passing through a surface having the area A is proportional to B*A. When an angle formed by a normal line of the plane and the magnetic field is θ, a flux is B*A*cos θ. That is, when the magnetic field and the plane are vertical to each other, the flux has the largest value as B*A and when the magnetic field and a surface area are parallel with each other, the flux has the smallest value as 0. Therefore, to effectively obtain the electromotive force induced by the flow of the magnetic fluid 100, there is a need to maximize the flux by controlling orientation of polarities of the magnetic fluid 100 which is located at an entrance portion 210 of the induction power generation unit 200, that is, letting magnetic pole directions agree with each other.
Further, ferrofluids may solve the problem in that magnetic property is lost due to a disorder of orientation of one-electrons inducing magnetism when a solid material having magnetism is melted and thus a liquid-phase magnet may not be obtained, and thus research and development into the ferrofluids for applying for other industrial facilities, household appliances, degradation of mobile phones, electric vehicles, and the like has been actively conducted.